1. Field of the Invention
The present invention relates to an antireflection structure used for preventing reflection of light in an optical apparatus or the like, a lens barrel including the antireflection structure, and a method for manufacturing the antireflection structure.
2. Description of the Background Art
Japanese Laid-open Patent Publication No. 2005-15309 discloses, as a method for improving light transmissivity of a light transmitting material, that a porous silica film is formed on a surface of the light transmitting material to realize a low refractive index. In Japanese Laid-open Patent Publication No. 2005-15309, the percentage of pores in the silica film is increased to substantially reduce the refractive index, and consequently, the Fresnel reflectance is reduced.
Meanwhile, Japanese Laid-open Patent Publication No. 2006-70254 discloses a method for forming a film having a fine pattern structure. In the method disclosed in Japanese Laid-open Patent Publication No. 2006-70254, a cast film is formed by casting a polymer solution on a casting belt, and the cast film is caused to have dew condensation. Then, an organic solvent in the polymer solution is volatilized first, thereby forming a film having a plurality of pores corresponding to a region occupied by condensed water drops.
Furthermore, Japanese Laid-open Patent Publication No. 2006-69207 discloses a film, a refractive index of which is reduced by forming a sponge-like three-dimensional structure on a surface of a base material. In Japanese Laid-open Patent Publication No. 2006-69207, a mixture obtained by mixing a template agent and an initiator into a polymer material is applied to a base material, and after the polymer material is cured, the template agent is dissolved and removed by using an organic solvent, thereby forming a sponge-like three-dimensional structure. The sponge-like three-dimensional structure substantially reduces the refractive index, thereby reducing the Fresnel reflectance at the film surface.
Furthermore, Japanese Laid-open Patent Publication No. 2002-60159 proposes a method for forming a fine structure such as a porous body. In this method, part of polymer chains, in a microlayer separation structure including a block copolymer or a graft copolymer, is resolved or cut, and then the resolved or cut polymer chains are removed by washing, thereby forming a fine structure such as a porous body.